Nickel-chromium sheet alloy



United States Patent 6 3,177,075 NICKEL-CHROMIUM SIEET ALLGY Edward G. Richards, Edgbaston, Birmingham, and

Ronald A. Smith, West Hagley, England, assignors to The International Nickel Company, inn, New York, N.Y., a corporation of Delaware No Drawing. Filed July 9, 1962, Ser. No. 208,576 Claims priority, application Great Britain, July 14, 1961, 25,665/ 61 3 Claims. (Cl. 75-171) The present invention is directed to nickel-base alloys having high creep strength at elevated temperatures on the order of 825 C. and above and, more particularly, to nickel-base creep resistant alloys which are capable of being rolled into sheet.

Articles and parts for use at high temperatures under mechanical stress, for example, in aircraft gas turbines, are produced in various ways, the three main production methods being machining from forged or extruded stock, precision casting and fabrication from sheet, usually by cold-forming and welding. This invention is concerned with materials for use in the last named method.

Such materials in addition to having a high creep stiength, i.e., a low rate of strain in secondary creep after solution heating and aging, must also be soft enough in the annealed condition to be readily cold-formed. If the hardness after annealing is too high, it is difficult to form the sheet into complicated components and also diificult to weld it under conditions of severe restraint. For this type of material high values of tensile and yield strength are not essential.

It is well known that nickel-chromium base alloys that contain molybdenum and also titanium and aluminum as hardening elements have excellent high temperature properties. The creep strength of such alloys generally increases as the total content of titanium and aluminum is increased but the hardness after annealing also increases and is unacceptably high at titanium and aluminum contents high enough to give adequate creep strength at temperatures of 825 C. and above, for example, a creep strain of less than 0.15% in 100 hours under a stress of 8.6 long tons per square inch at 840 C.

Those skilled in the art will appreciate that while man nickel-base alloys are currently available which have high creep strength at temperatures on the order of 825 C. and above, these alloys are diflicult to form into acceptable mill products, including sheet and the like, since the alloying elements which are included in the alloys for the purpose of contributing high creep strength thereto markedly reduce the workability of these alloys. Accordingly, many of the commercial creep resistant alloys can only be made available in the form of castings. Many other commercial nickel-base creep resistant alloys can only be made available as forgings since the alloys may be formed while hot but cannot be formed while cold in the usual mill processing equipment. many structural parts, including tail pipes, after-burner systems of aircraft gas turbine engines, must be fabricated from sheet materials since these articles by their very nature cannot be produced satisfactorily from mill shapes having other forms. It is to be appreciated that alloys which may successfully be converted into sheet must possess a commercial degree of hot workability and cold workability. As those skilled in the art of course appreciate, with presently available equipment, it is notcommercially feasible to produce sheet by the extrusion and/or hot forging processes. The art, accordingly, has been faced with the vexing problem of providing in a single alloy a suflicient commercial degree of hot workability and cold workability to enable working of the alloy into sheet form while at the same time providing However,

3,177,075 Patented Apr. 6, 1965 in the final sheet product sufficiently high creep strength to enable the final fabricated part to withstand the combinations of stress and temperature to which it is subjected In use.

We have now found that the presence of cobalt in amounts exceeding 20% in alloys of the kind just mentioned increases the creep strength of the alloy but does not markedly increase the hardness after annealing of sheet made from the alloy. The hardness may even be decreased.

It is an object of the present invention to provide nickelchromium alloys having high creep strength at elevated temperatures on the order of 825 C. and higher.

It is a further object of the present invention to provide nickel-chromium alloys capable of being rolled into sheet.

A still further object of the present invention is to provide special nickel-chromium alloys having high creep strength at elevated temperatures, which are capable of being rolled into sheet, and which are readily weldable.

Other objects and advantages of the invention will become apparent from the following description.

Alloys according to the invention contain, in percent by weight, from 18% to 20% chromium, 25% to 40% cobalt, 3% to 8% molybdenum, 0.04% to 0.1% carbon, 2% to 2.75% titanium, about 0.7% or 0.75% to 1.3% aluminum, 0% to 0.004% boron, e.g., about 0.001% to 0.004% boron, 0% to 0.1% zirconium, e.g.,

. about 0.01% to 0.1% Zirconium, the balance being nickel.

The cobalt content may suitably be from 28% to 32% and the molybenum content from 3% or 3.5% to 5.5%, and preferably the zirconium content does not exceed- 0.05%. For optimum weldability the boron content should be as low as practicable, and preferably does not exceed 0.003%. The alloy may also include small amounts of usual incidental elements and impurities found in alloys of this character. Thus, the alloy may contain up to about 0.5% silicon, up to about 1% manganese and up to about 5% iron. It is to be understood that when the expression balance essentially nickel is employed herein, such amounts of these incidental elements and other unavoidably present impurities are included thereby.

By Way of example, alloys of the compositions set out in Table I below were formed into sheet 18 S.W.G. (0.048 inch) thick, and their hardness was measured after annealing for ten minutes at 1150 C. and waterquenching:

Table 1 Nominal Composition (percent by wt.) Hard- Alloy No. ness 4 (DPN) C Cr Co Mo Ti Al Ni 20 14 5 2 l Bal. 211 20 30 5 2 1 Bal. 186 20 30 5 2. 3 1. 2 Bal. 209

Creep tests were then performed on test pieces cut from the sheets and solution treated and aged, those of Alloy No. A (outside the present invention) being solution heated at 0 C. for five minutes, water-quenched, and aged at 750 C. for 16 hours and those of Alloys Nos. 1 and 2 (Within the present invention) being solution heated at 1180 C. for ten minutes and then air cooled and aged at 840 C. for 16 hours. Alloy No. A showed a strain of 0.1% in 10 0 hours under a stress of only 7.8 long tons per square inch at 780 0., whereas under the more severe conditions of 8.6 long tons per square inch stress at 840 C., Alloy No. 1 showed only 0.12% strain in 96 hours and Alloy No. 2 showed 0.05% strain in 96 hours.

Alloys provided in accordance with the invention should beheat treated to develop optimum creep properties.

therein. Thus, the alloys may besubjected to a solution treatment in theprange of about 1100 C. to about 1200 C. for about 2 to 30 minutes in usual sheet sections. This treatment may be followed by aging at650 C. to 850 C. or 900 C. for about 2 to 16 hours.

The alloys are readily weldable by means of any of the usual welding techniques employed for nickel-chromium alloys including electric arc weldingwith or without the use of filler metal and including shielded-arc welding and flash-butt welding. The alloys may be welded in the solution-treated condition or in the solution-treated and Examples of fabricated-parts for which the alloys are useful are'tail pipes and after-burner systems'of aircraft gas turbine engines for which high creep strength is of paramount importance.

Although the present invention has beendescribed in conjunction with preferred embodiments, it'isto be under'stood that modifications and variations may be resorted to without departing from the spirit and scope of the aged'condition. Assemblies welded in the solution-treat- 1 ed condition can be aged after welding.

To illustrate the advantageous properties obtainable in Welded structures fabricated from alloys according to C. and water quenched before. welding and aged for 4 hours at 750 C. after welding. Alloys No. 1 and No. 2 were tested as 0.030-in. thick sheet annealedfor minutes at 1150" C. and air-cooled before welding and finally aged after welding for 4 hours at 900 C.

The results are set forth in Table II below:

rolled into sheet and consisting essentially'of about 18% to %chromium, about to cobalt, about 3% to 8% molybdenum, about 0.04%,to about 0.1% carbon, about 2% to 2.75% titanium, about 0.7% -to:l.3% aluminum, up to about 0.004% boron, up to about 0.1% zirconium, and the balance essentially nickel. I

2. A weldable nickel-base alloy characterized by a creep strain in 96 hours of less than 0.15% at a stress of 86 long tons per square inch and 840 C;, capable of being rolledinto sheet and consisting essentially of. about 18% to 20% chromium, about 28% to-32%.coba1t, about 3% a to 5.5% molybdenum, about 0.04% to 0.1% carbon, about 2% to2.75% titanium, about 0.75% to 1.3% aluminum, up ,to about 0.004%,boron, upto about 0.05% zirconium and thebalance esesntially nickel.

Table II Alloy No. A Alloy N0. 1 Alloy N0. 2

Test Temp, C.

U.T.S., Y.S., Elong, U.T.S., Y.S., El0ng., U.T.S.,' Y.S., El0ng.,

t.s.i. t.s.i. Percent t.s.i. t.s.i. Percent t.s.i. t.s.i. Percent 7s 4s 20 46 V 22 3'5 51 27 20 37 4 34 15 30 36 23 15 39 33 6 26 20 11 34 25 8 1 Y.S.yleld stress.

It will be observed that Alloys Nos. 1 and .2 had substantially higher ductility at elevated temperaturesthan Alloy A. Aspointedout above, the most important properties of alloys for usein the form of sheet are ductility and creep strength, and the somewhat lower tensile Alloy A are not of importance.

The/alloys can be produced in the usual melting equip- 'ment' employed for melting alloys vof the same general nature. It is advantageous to produce ingots of the alloy by vacuum melting and vacuum casting. Usual metalworking equipment is employed to break down the ingots by hot working and the hot-worked alloy is rolled. to sheet without difficulty by means of the usual cold rolling mills.

and yield stresses of Alloys Nos. 1 and 2 compared. with 3. An alloy as claim 2 which contains about 0.001% to 0.003 boron, about 0.01% to about 0.05% zirconium, and in which the molybdenum; content is from 3.5% to 5.5%. i

' ReferencesCited :by the Examiner UNITED STATES PATENTS 2,766,155 10/56 Betteridgeet al.. 171 2,793,108- 5/57 Franklin 75 171 2,920,956 1/60 Nisbet'et a1. 75 171 2,977,222 3/61 Bieber 75-171 DAVID L. RECK, Primary Examiner. V

Gresham .et al. 75-171 7 

1. A WELDABLE NICKEL-BASE ALLOY CHARACTERIZED BY A CREEP STRAIN IN 96 HOURS OF LESS THAN 0.15% AT A STRESS OF 8.6 LONG TONS PER SQUARE INCH AND 840*C., CAPABLE OF BEING ROLLED INTO SHEET AND CONSISTING ESSENTIALLY OF ABOUT 18% TO 20% CHROMIUM, ABOUT 25% TO 40% COBALT, ABOUT 3% TO 8% MOLYBDENUM, ABOUT 0.04% TO ABOUT 0.1% CARBON, ABOUT 2% TO 2.75% TITANIUM, ABOUT 0.7% TO 1.3% ALUMINUM, UP TO ABOUT 0.004% BORON, UP TO ABOUT 0.1% ZIRCONIUM, AND THE BALANCE ESSENTIALLY NICKEL. 